Thermal switches



y 9, 1956 R. w. DE LANCEY 2,748,222

THERMAL SWITCHES Filed Aug. 11, 1953 fi/Mirm M kw ATTORNEY United States Patent THERMAL SWITCHES Ralph W. De Lancey, Meriden, Conn.

Application August 11, 1953, Serial No. 373,471

4 Claims. (Cl. 200122) The present invention relates to thermal switches and is more particularly directed to remote controlled thermal switches employing an electric heater.

In many arts such, for example, as the fuel burner control art, it is desirable to elfect the closing of a normally open, or the opening of a normally closed local circuit in response to the closing or opening of a circuit including a heater. These devices operate as thermal relays, or the heater and bimetallic elements in a normally closed circuit device may be connected in series.

The present invention contemplates such thermal relays wherein the heat responsive, bimetallic elements are received in a tubular resistance heater, so that they may be heated by radiant heat from a resistance element requiring relatively low wattage input, and are protected against rapid cooling by the convection currents usually found in thermal relays where there is freedom of air movement.

According to the present invention, the conducting and insulating parts, as well as the support for the heater, are preferably in the form of stack held together by bolts. Such an assembly facilitates manufacture and assembly of the component parts.

The accompanying drawings show, for purposes of illustrating the present invention, several embodiments in which the invention may take form, it being understood that the drawings are illustrative of the invention rather than limiting the same.

In the accompanying drawings:

Figure 1 is a perspective view of one form of complete thermal switch;

Figure 2 is a longitudinal sectional view of the switch of Figure 1 illustrating a normally open switch;

Figure 3 is a view similar to Figure 1, showing a modified form of construction;

Figures 4 and 5 are transverse and longitudinal sectional views on the lines 4-4 and 5-5, respectively, of the switch of Figures 3 and 6;

Figure 6 is a fragmentary view illustrating a normally closed switch also showing the heater in series with the bimetallic elements.

In Figures 1 and 2 of the drawings, the bimetallic members are indicated at 10 and 11 and the heater at 12. This heater is in the form of a ceramic body 13 with a resistance winding 14. The heater is carried by a relatively stiff metallic support 15 having a clip 16 at one end. The bimetal members have broadened bases 17 and 18, as indicated more clearly in Figure 1, and are provided with soldering lugs indicated at 17' and 18' for circuit wires 19 and 20. The bimetal members, the mounting bracket 15 and two metal terminal plates 21 and 22 have soldering lugs 21 and 22', respectively, are mounted in a stack of insulating plates 23, 24, 25, 26, 27, 28, 29, 3t and 31 so as to be insulated from one another. The metal members and insulating members are punched to have holes 32 and receive insulating tubes 33 and the stack is clamped together by bolts 34 so as to form a solid body in which all the conducting parts are held fixed and thoroughly insulated from one another.

The insulating plate 23 has an extension as indicated at 35 which carries a screw 36 adapted to bear upon the bimetal element 11 so as to adjust the spacing of the bimetal elements. As shown in Figure l, the soldering lugs 21' and 22 are connected by wires 37 and 38 to the terminals 39 and 46) of the resistance winding 14-. The soldering lugs 21 and 22' are also connected to current supplying leads 41 and 42 so that the heater can be connected into an external circuit.

In the construction indicated in Figures 1 and 2, the contacts 43 and 44 on the ends of the bimetal members it) and 11 are separated so that the circuit controlled by the bimetal elements is open. This would be a normal condition Where a normally open circuit heater is used to control a normally open secondary or relay circuit. ln such cases the adjacent faces of the bimetal elements carry the component having a lower coeflicient of expansion. Closing the circuit to energize the resistance coil in the heater will quickly warm the heater and heat will radiate to the bimetal elements, causing them to approach and close, and they will remain closed as long as the heater is kept Warm.

in the form shown in Figures 3, 4 and 5, corresponding parts have the same reference characters as in Figures 1 and 2. Here a housing member 45 made of sheet metal is secured to the stack (17', 18, 232S) in the same Way as the bracket 15. An insulating plate 46 secured to the housing supports the heater 1?. and its supply leads 37, 33. The housing has mounting flanges 47.

While two bimetallic members are preferred, it is possible at a sacrifice of quickness of operation to employ one metallic strip and an ordinary metal conducting strip.

Figure 6 illustrates a form of construction in which the bimetal elements it) and 11 are reversed with respect to one another and have the contacts 43 and 44' normally closed. Supplying current to the resistance heater 14 will then cause the contacts to separate and open the secondary or control circuit. Where the contacts are normally closed as in Figure 3, it is possible to connect the resistance coil lid and contacts in series, as indicated by the wires 50. The external leads are indicated at 51 and 52.

Since it is obvious that the invention may be embodied in other forms and constructions within the scope of the claims, I wish it to be understood that the particular forms shown are but several of these forms, and various modifications and changes being possible, i do not otherwise limit myself in any way with respect thereto.

What is claimed is:

1. A thermal switch comprising a tubular resistance heater provided with terminals, a heater support, two metallic strips having narrowed portions in the heater provided with contacts for controlling a circuit and widened mounting portions, at least one of the strips being bimetallic, a pair of terminal plates, wires connecting the terminal plates with the heater terminals, a plurality of insulating places between which the bracket, the widened portions or the metallic strips, heater support and the terminal plates are interposed, and bolts for clamping the insulating plates and interposed parts into stack.

2. A thermal switch such as claimed in claim 1, wherein one of the insulating plates carries an adjusting screw bearing on one of the metallic strips to adjust the spacing of the contacts.

3. A thermal switch comprising a plurality of insulating and conducting plates clamped together to form a rigid stack with the conducting plates insulated from one another and having contact carrying extensions beyond the insulating plates, at least one of the conducting plates being bimetallic, one of the plates having an extension forming a bracket adjacent the contact carrying extension, a tubular resistance heater supported in the bracket and about the bimetallic extension so as to heat the same, and leads connecting the ends of the resistance heater with two other of said conducting plates.

4. In combination, a plurality of insulating and metal plates each provided with uniformly spaced holes in alignment with one another, insulating tubes extending through the aligned holes, clamping bolts in the tubes, one of the metal plates extending beyond the insulating plates, a tubular resistance heater carried by the first mentioned metal plate, two of the metal plates having soldering lugs, lead wires connecting the soldering lugs and the windings of the resistance heater, and another two of said metallic plates, one of which is bimetallic, having contactcarrying extensions inside the heater.

UNITED STATES PATENTS Birsfield Sept. 13, 1910 Thomas Aug. 14, 1934 Harris July 8, 1941 Ludwick July 25, 1944 Dietz Jan. 17, 1950 Miller June 3, 1952 Jackel Sept. 16, 1952 Alexander Sept. 30, 1952 FOREIGN PATENTS Great Britain Mar. 23, 1939 

